Fix FFmpeg initialization logic

[mthrok]

Differential Revision: D47398447

[pytorch-bot]

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❌ 7 New Failures

As of commit e4d5364:

NEW FAILURES - The following jobs have failed:

• build (3.8) (gh)
• Build Windows Conda (gh)
• pytorch/audio / manywheel-py3_8-cuda11_8 (gh)
• pytorch/audio / manywheel-py3_8-cuda12_1 (gh)
• tests (3.10) / linux-job (gh)
• tests (3.8) / linux-job (gh)
• tests (3.9) / linux-job (gh)

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This pull request was exported from Phabricator. Differential Revision: D47398447

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This pull request has been merged in 49e269a.

[github-actions]

Hey @None.
You merged this PR, but labels were not properly added. Please add a primary and secondary label (See https://github.com/pytorch/audio/blob/main/.github/process_commit.py).

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